How does prostaglandin bring a mare into heat, and can you give repeated shots if one cycle is missed?

There have been numerous research studies regarding the use of prostaglandin (PG). When the mare ovulates, the follicle ruptures to release the egg. The structure that grows back in the area of the rupture is called a Corpus Luteum (CL) which produces progesterone, the hormone that tells the mare she is pregnant. Once a functional CL is present (generally 4-5 days following ovulation), PG will work and bring the mare back into heat without any complication or future risk for the mare. All the PG is doing is causing the regressing of the CL and therefore allowing the mare to return to heat within approximately 3 to 4 days. Mares will have a normal heat cycle and develop a follicle to produce the egg for fertilization.